Cartographic indicators showing the image of a geographical map to the pilots of certain craft are increasingly used, especially in the aeronautical field.
Thus, our invention more particularly relates to an aerial-navigation electronic indicator. A cartographic indicator is essentially used for providing the aircraft pilot with a geographical map of the overflown area. The traverse of the displayed area corresponds to the flight path and its positioning is dependent on the longitude and latitude of the aircraft and also, optionally, on its heading. In addition to the geographical map, the navigation device jointly displays markings and symbols for indicating the current position of the aircraft, as well as navigational data (speed, fuel consumption, route to be taken, etc.).
In the case of a map recorded on an optical support such as a photographic color film, a reader analyzing same comprises a spectral separator followed by photoelectric detectors or sensors, three of them being conventionally provided for producing the red (R), green (V) and blue (B) video signals necessary for the color presentation. Each of these detectors functions in a given spectral band and comprises either a television camera or a photomultiplier, depending on whether the reader uses a single light source or a flying-spot tube for transluminating the film. Apart from the detectors, the reader comprises circuits for controlling the cameras or the flying-spot tube, as well as video-amplification circuits.
In systems using a magnetic support (video disk or tape) as a recording medium, it is also necessary to preserve the distribution of the three basic colors on the support in order to enable the extraction of the corresponding video channels.